CN113245365A - Rolling production method for improving toughness of steel products on line - Google Patents
Rolling production method for improving toughness of steel products on line Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/16—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling wire rods, bars, merchant bars, rounds wire or material of like small cross-section
- B21B1/18—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling wire rods, bars, merchant bars, rounds wire or material of like small cross-section in a continuous process
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
- B21B45/004—Heating the product
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
- B21B45/02—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for lubricating, cooling, or cleaning
- B21B45/0203—Cooling
- B21B45/0209—Cooling devices, e.g. using gaseous coolants
- B21B45/0215—Cooling devices, e.g. using gaseous coolants using liquid coolants, e.g. for sections, for tubes
- B21B45/0224—Cooling devices, e.g. using gaseous coolants using liquid coolants, e.g. for sections, for tubes for wire, rods, rounds, bars
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
- B21B45/04—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing
- B21B45/08—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing hydraulically
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Abstract
The invention discloses a rolling production method for improving the toughness of steel products on line, which takes continuous casting billets as raw materials and sequentially comprises the following working procedures: heating a blank, descaling, rough rolling, continuous rolling, water cooling, finish rolling of a bar reducing and sizing unit and cooling of a cooling bed to finally obtain a finished bar; and cooling the continuously rolled bar to 650-850 ℃ in water, and after cooling in water, returning the rolled bar to red to obtain the finish rolling temperature of the bar reducing and sizing mill unit, wherein the finish rolling temperature is 500-700 ℃, and the temperature of a cooling bed on the bar is 480-650 ℃. According to the invention, the bar material reducing and sizing mill set adopts KOCKS rolling for finish rolling, proeutectoid ferrite in a non-required form is eliminated by controlling the finish rolling temperature and the cooling temperature after rolling, the toughness of the steel is improved, and the control on the grain size, hardness and mechanical property of non-quenched and tempered steel can be realized by adopting the rapid cooling technology after rolling.
Description
Technical Field
The invention belongs to the field of special steel production and processing in the metallurgical industry, relates to a rolling process, and particularly relates to a method for improving the toughness of steel.
Background
In recent years, with the rapid development of economy in China, the automobile manufacturing industry and the machinery manufacturing industry in China are rapidly developed, and under the background, the consumption and the variety of non-quenched and tempered steel are increased day by day, and the quality requirement on the non-quenched and tempered steel is gradually improved. The non-quenched and tempered steel has better mechanical property, more uniform hardness from the center to the edge, longer fatigue life, greatly reduced manufacturing cost and wide application in manufacturing high-strength rod parts and shaft parts. However, since the finish rolling temperature (generally 800 to 850 ℃) of non-heat treated steel is high, the austenite grain size is liable to be large, proeutectoid ferrite of an undesirable form, i.e., acicular ferrite and network ferrite, is liable to be formed, which affects the toughness of the steel and reduces the service life of the steel.
Quenched and tempered steel is one of the most widely used important materials in the machine manufacturing industry. Generally, methods for improving the impact toughness of quenched and tempered steel include: improving partial alloy content of materials, such as nickel, copper and the like; or purifying the molten steel, reducing the impurity content of the material and achieving the purpose of improving the toughness of the part. However, in the current technology, increasing the alloy content increases the cost, is not favorable for resource saving and is at a disadvantage in market competition. The potential for purifying molten steel is limited and requires more complex processes and expensive filtration accessories. Patent CN 103993139 a discloses a method for improving the impact toughness of quenched and tempered steel, which improves the impact toughness of the quenched and tempered steel by improving the heat treatment process, but the patent does not mention the method for improving the toughness of non-quenched and tempered steel on line.
After being forged, the 20CrMnTiH gear steel piece is easy to form non-equilibrium structures such as acicular ferrite, reticular ferrite, bainite and the like after being cooled because austenite grains are coarse, and the subsequent carburization treatment and cutting processing are influenced. The influence of multi-step continuous isothermal normalizing on the microstructure and the performance of the forged 20CrMnTiH steel is researched in the document (Liu Cheng, Yang Cheng, Zhao Sha Bo, Huagao and the like, and the metal heat treatment [ J ].2017,42(8):93-97), the influence of the multi-step continuous cooling isothermal normalizing on the microstructure and the hardness of the forged 20CrMnTiH steel blank is researched, and the form, the forming conditions and the control method of the proeutectoid ferrite in the steel are discussed. The result shows that the pro-eutectoid ferrite form in the steel can be accurately controlled by adopting a proper continuous cooling isothermal normalizing process, so that the forging stock can obtain the required ferrite plus pearlite structure, the grain size can be controlled within 4-6 grades, and the hardness is within the range of 160-190 HBW. However, the document does not mention the hot rolling on-line control process, nor the control method of the non-tempering steel.
Through literature search, in the prior art, for improving the toughness of steel, most steel enterprises only improve the impact toughness of the steel through a heat treatment process of quenched and tempered steel, and related technical reports that the toughness of the steel is improved through researching hot rolled steel and the toughness of the steel is improved through researching rapid cooling after rolling of the steel are not found at present.
Disclosure of Invention
In order to save the heat treatment cost of steel and shorten the contract delivery cycle, the invention provides a rolling production method for improving the toughness of steel on line, which mainly eliminates proeutectoid ferrite in a non-required form by controlling the cooling temperature after rolling and improves the toughness of steel.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a rolling production method for improving the toughness of steel products on line takes a continuous casting billet as a raw material, and sequentially comprises the following working procedures: heating a blank, descaling, rough rolling, continuous rolling, water cooling, finish rolling of a bar reducing and sizing unit and cooling of a cooling bed to finally obtain a finished bar; wherein the content of the first and second substances,
in the bar reducing and sizing mill set finish rolling procedure, a rolled bar obtained in the water cooling procedure is subjected to finish rolling by using a bar reducing and sizing mill set to obtain a bar; the finishing temperature is 500-700 ℃.
In the above rolling production method, as a preferred embodiment, in the slab heating step, the slab is heated, and the soaking temperature is 1100 to 1180 ℃ (for example, 1110 ℃, 1120 ℃, 1130 ℃, 1140 ℃, 1150 ℃, 1160 ℃, 1170 ℃, 1175 ℃).
In the rolling production method, as a preferred embodiment, in the billet heating step, the total heating time from the time when the billet enters the heating furnace to the time when the billet leaves the heating furnace is 4 to 6 hours, the soaking time in the soaking section is 60 to 100min, and preferably, the heating step is performed in a four-section stepping heating furnace.
In the above rolling production method, as a preferred embodiment, the raw material of the continuous casting slab is any one of 40MnV medium carbon steel, 42CrMo medium carbon steel, 45 medium carbon steel, and 40Cr medium carbon steel.
In the rolling production method, as a preferred embodiment, in the blank heating process, the heat preservation temperature of the soaking section is 1150-1180 ℃, and the soaking time of the soaking section is 60-80 min.
In the rolling production method, as a preferred embodiment, in the descaling process, high-pressure water is used for descaling to remove scale, and the pressure of the high-pressure water is 26-30 MPa; preferably 40 to 50 MPa.
In the rolling production method, as a preferred embodiment, in the rough rolling process, the inlet temperature is 980-1050 ℃, and the rough rolling pass is 5-7; preferably, the roughing mill used in the roughing step has 6 stands in total, and the number of roughing passes is 6.
In the rolling production method, as a preferred embodiment, the continuous rolling process includes an intermediate rolling process and a pre-finish rolling process, and a rolled material suitable for entering the bar reducing and sizing mill set is obtained after the continuous rolling.
In the rolling production method, as a preferred embodiment, the inlet temperature of the intermediate rolling process is 900 to 950 ℃, and the intermediate rolling pass is 5 to 7; preferably, in the intermediate rolling step, a 6-stand intermediate rolling mill is provided, and the intermediate rolling pass is 6 passes.
In the rolling production method, as a preferred embodiment, in the pre-finish rolling step, the number of pre-finish rolling passes is 3 to 5; preferably, 4 pre-finishing mills are arranged in the pre-finishing rolling process, and the pre-finishing pass is 4 passes.
In the rolling production method, as a preferred embodiment, in the water cooling process, the rolled material after continuous rolling is cooled to 650 to 850 ℃ by water; preferably, the water cooling speed of the through water cooling is 35-100 ℃/s (for example, 40 ℃/s, 50 ℃/s, 60 ℃/s, 70 ℃/s, 80 ℃/s and 90 ℃/s), and the water pressure is 0.4-0.8 MPa (for example, 0.5MPa, 0.6MPa, 0.7MPa and 0.75 MPa).
In the above rolling production method, as a preferred embodiment, in the through-water cooling step, after the through-water cooling, the rolled material is returned to red to obtain the temperature of the finish rolling of the bar reducing and sizing mill group, so that the rolled material suitable for the finish rolling of the bar reducing and sizing mill group is obtained.
In the invention, the water cooling process aims at reducing the rolling temperature, realizing low-temperature rolling and improving the structure and comprehensive mechanical properties of the bar.
In addition, the water cooling is the online water cooling in the rolling process, so that the rolling production process is simplified.
In the rolling production method, as a preferred embodiment, in the finish rolling process of the bar reducing and sizing mill unit, the initial rolling temperature is 800-900 ℃; preferably, the bar reducing and sizing mill group finish rolling is KOCKS rolling.
The invention adopts lower finishing temperature to prevent coarse austenite grain size, and adopts forced cooling process after finishing to form pro-eutectoid ferrite with required form.
In the rolling production method, as a preferred embodiment, the cooling bed cooling step further comprises a second water through cooling step; and (3) after the bar material obtained by the finish rolling of the bar material reducing sizing machine set is cooled by the second through water, the bar material is put on a cooling bed in a low-temperature state to be cooled by the cooling bed. The second water-through cooling is still online water-through cooling; preferably, the water cooling speed of the second water passing cooling is 35-100 ℃/s (for example, 40 ℃/s, 50 ℃/s, 60 ℃/s, 70 ℃/s, 80 ℃/s and 90 ℃/s).
In the rolling production method, as a preferred embodiment, the temperature of the cooling bed on the bar is 480-650 ℃.
In the rolling production method, as a preferred embodiment, the cooling bed cooling adopts a slow cooling mode (for example, air cooling), and the cooling speed of the cooling bed is more than or equal to 20 ℃/min; preferably, the surface temperature of the cooling bed below the bar is less than or equal to 200 ℃ during cooling of the cooling bed.
In the above rolling production method, as a preferred embodiment, in the cooling bed cooling step, the bar material obtained after the finish rolling by the bar material reducing and sizing mill group may be subjected to cooling bed air cooling, if conditions permit.
In the rolling production method, as a preferred embodiment, the finished bar has a specification (bar diameter) of 50-130 mm (for example, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120 mm).
The steel obtained by the rolling production method does not need to be tempered and is non-tempered steel.
The invention adopts the technical principle of improving the toughness of steel products on line to produce non-quenched and tempered steel: the non-quenched and tempered steel grade eliminates proeutectoid ferrite in a non-required form by controlling the finish rolling temperature and the cooling temperature after rolling, and improves the toughness of the steel.
According to the invention, the KOCKS post-rolling strong cooling process is utilized, the time for precipitation of the non-eutectoid ferrite is controlled, so that austenite has sufficient time for precipitation of the proeutectoid ferrite in the early stage of strong cooling, the temperature for precipitation of the ferrite is high, the time is long, the atomic diffusion during phase change is facilitated, the formation and precipitation of the bulk ferrite are facilitated, a pseudo-eutectoid P region is formed, the microstructure form of the bulk ferrite and pearlite is obtained after complete transformation, and the precipitation formation of the reticular and acicular ferrite is avoided; thereby achieving the purpose of improving the toughness of the steel.
In the invention, the technical characteristics can be freely combined to form a new technical scheme under the condition of not conflicting with each other.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention reduces heating energy consumption, saves production cost and protects environment by optimizing the heating process system of the heating furnace.
(2) The rolling production method provided by the invention realizes the control of the grain size, hardness and mechanical property of the non-tempered steel by adopting the rapid cooling technology after rolling, and the control of the grain size, hardness and mechanical property of the non-tempered steel by the method is superior to that of the conventional rolling technology.
Drawings
FIG. 1 is a hot-rolled metallographic structure of 40MnV non-heat-treated steel obtained in example 1 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The rolling production method for improving the toughness of the steel on line is suitable for rolling production of non-quenched and tempered steels such as 40MnV medium carbon steel, 42CrMo series medium carbon steel, 45 medium carbon steel, 40Cr medium carbon steel and the like. The rolling production method for improving the toughness of the steel on line provided by the invention is explained in detail by taking the non-tempered steel 40MnV material as an example.
In the non-tempered steel 40MnV material, silicon and manganese are main additive elements of the 40MnV steel, and play roles in improving the body strength and the hardenability of the steel. The addition of vanadium makes the crystal grains in the steel refined, can prevent the crystal grains from growing during carburization, and improves the strength and toughness of the steel.
The invention provides a rolling production method for improving the toughness of steel products on line, which takes the raw material of a 40MnV non-tempered steel continuous casting billet as an example, and sequentially comprises the following working procedures: heating, descaling, rough rolling, continuous rolling, water cooling, bar reducing sizing mill set finish rolling and cooling bed cooling, and finally obtaining the finished bar.
Wherein, the raw material of the 40MnV non-tempered steel continuous casting billet is obtained by conventional smelting, refining and continuous casting processes, and is not described in detail here.
The rolling production method comprises the following specific steps:
(1) heating a steel billet: heating the 40MnV non-tempered steel continuous casting billet. The temperature of the soaking section is 1150-1180 ℃ (for example, 1155 ℃, 1160 ℃, 1165 ℃, 1170 ℃, 1175 ℃); preferably, the total heating time from the blank entering the heating furnace to the blank leaving the heating furnace is 4-6 h (for example, 4.5h, 5.0h and 5.5h), and the soaking time of the soaking section is 60-100 min (for example, 65min, 70min, 75min, 80min, 90min and 95 min); preferably, the heating process is performed in a four-stage step furnace.
(2) Descaling a steel billet: descaling the heated steel billet by adopting high-pressure water to remove scale on the surface of the steel billet to obtain a descaled steel billet; the pressure of the high-pressure water is 26-30 MPa (for example, 27MPa, 28MPa, 29 MPa); preferably 40 to 50MPa (42MPa, 44MPa, 45MPa, 47MPa, 49 MPa).
(3) Rough rolling of a steel billet: sending the descaled steel billets into a high-rigidity roughing mill for 6 frames for roughing to obtain rough rolling billets; the number of roughing mills used in the roughing step was 6 in total. Preferably, the entry temperature of the slab into the roughing mill during rough rolling is 980 to 1050 ℃ (e.g., 990 ℃, 1000 ℃, 1010 ℃, 1020 ℃, 1025 ℃, 1030 ℃, 1040 ℃), and the number of rough rolling passes is 6.
(4) Continuous rolling by a continuous rolling unit: sending the rough rolling blank obtained in the step (3) into a continuous rolling unit for medium rolling and pre-finish rolling; the temperature of the rough rolling blank at the middle rolling inlet is 900-950 ℃ (for example, 905 ℃, 910 ℃, 920 ℃, 930 ℃ and 940 ℃), the middle rolling pass is 6 passes, and the pre-finish rolling pass is 4 passes.
(5) Cooling through water: and (3) carrying out water cooling on the pre-finish rolled material, and after the water cooling, enabling the rolled material to return to red to obtain the temperature of the KOCKS rolling. Preferably, the surface temperature of the rolled material is cooled to 650 to 850 ℃ by water cooling, and more preferably to 650 to 800 ℃ (for example, 675 ℃, 700 ℃, 725 ℃, 750 ℃, 775 ℃, 790 ℃).
(6) And (3) KOCKS rolling: performing KOCKS rolling on the rolled material obtained in the step (5) to obtain a bar material; preferably, the initial rolling temperature of the KOCKS rolling is 800 to 900 ℃ (e.g., 810 ℃, 820 ℃, 830 ℃, 840 ℃, 850 ℃, 860 ℃, 870 ℃, 880 ℃, 890 ℃) and the final rolling temperature is 500 to 700 ℃ (e.g., 520 ℃, 550 ℃, 580 ℃, 600 ℃, 625 ℃, 650 ℃, 670 ℃, 680 ℃, 690 ℃).
(7) Cooling by a cooling bed: and controlling the temperature of the bar after the bar is rolled by the KOCKS to be 500-700 ℃, cooling the bar obtained after the bar is rolled by the KOCKS through water for the second time, and controlling the bar to be put on a cooling bed at a low temperature for cooling in the cooling bed. The temperature of the cooling bed on the bar is 480-650 ℃ (for example, 500 ℃, 520 ℃, 550 ℃, 600 ℃, 620 ℃ and 640 ℃); the surface temperature of the bar material in the cooling bed is less than or equal to 200 ℃, the cooling bed adopts a slow cooling mode, the cooling speed is more than or equal to 20 ℃/min (for example, 25 ℃/min and 30 ℃/min), and the preferable range is 20-30 ℃/min (for example, 25 ℃/min); preferably, the surface temperature of the cooling bed below the bar is less than or equal to 200 ℃ during cooling of the cooling bed.
Example 1
The rolling production method for improving the toughness of the steel products on line provided by the embodiment takes a 40MnV non-tempered steel continuous casting blank as a raw material, and obtains a finished product 40MnV steel with the specification of 50mm through rolling production, and the rolling production method comprises the following steps:
step 1: cutting the continuous casting billet with the diameter of 300 multiplied by 400 multiplied by 9000mm, and putting the continuous casting billet into a heating furnace for reheating by adopting a cold conveying or red conveying mode.
Step 2: heating a steel billet: heating the steel billet by adopting a four-section heating mode, wherein the temperature of the heating second section meets the process requirement (namely 1100-1150 ℃); the temperature of the soaking section is 1160 ℃; the total heating time in the heating procedure is 5h, and the soaking time in the soaking section is 70 min.
And step 3: descaling a steel billet: descaling the heated billet by adopting high-pressure water to remove scale; the pressure of the high-pressure water is 45 MPa.
And 4, step 4: rough rolling of a steel billet: sending the descaled steel billets into a high-rigidity roughing mill (6 stands) for roughing rolling to obtain roughing rolling billets; the surface temperature of the rough rolling blank at the rough rolling inlet is 1000 ℃, and the rough rolling pass is 6.
And 5: continuous rolling by a continuous rolling unit: sending the rough rolling blank obtained in the step 4 into a continuous rolling unit for medium rolling and pre-finish rolling to obtain a rolled material with the specification of 70 mm; the surface temperature of the rough rolling blank at the middle rolling inlet is 950 ℃, the middle rolling pass is 6 passes, the pre-finish rolling outlet temperature is 920 ℃, and the pre-finish rolling pass is 4 passes.
Step 6: cooling through water: and (3) carrying out water cooling on the rolled material after pre-finish rolling, and controlling the surface temperature of the rolled material to be cooled to 800 ℃. After water cooling, the rolled stock was red back to obtain the temperature for KOCKS rolling. In this example, the water cooling rate of the water-through cooling was 50 ℃/s, and the water pressure was 0.8 MPa.
And 7: and (3) KOCKS rolling: performing KOCKS rolling on the rolled material which returns to red after water cooling to obtain a bar material with the specification of 50 mm; the initial rolling temperature of the KOCKS rolling is 830 ℃, the temperature requirement of entering a KOCKS rolling mill is met, and the final rolling temperature is 580 ℃.
And 8: cooling by a cooling bed: and (4) rolling the bar material with the specification of 50mm obtained in the step (7), cooling the bar material with water for the second time, and then air-cooling the bar material on a cooling bed at a low temperature to finally obtain a finished bar material. Wherein the temperature of the upper cooling bed of the bar is 500 ℃, the temperature of the lower cooling bed of the bar is 200 ℃, and the bar is air-cooled on the cooling bed.
By adopting the rolling production method provided by the embodiment, the hot-rolled structure of the obtained 40MnV non-quenched and tempered steel is ferrite plus pearlite, as shown in FIG. 1, the grain size is 8 grades, and the hardness is 285 HBW; the mechanical properties of the hot-rolled bar of this example were tested with reference to national standard GB/T15712-2016, and the mechanical properties of the bar product are shown in Table 1. Wherein the impact absorption work is obtained at room temperature in a V-type impact.
TABLE 1 mechanical Properties of 40MnV non-quenched and tempered steel bar product obtained in example 1
Example 2
The rolling production method for improving the toughness of the steel products on line provided by the embodiment takes a 40MnV non-tempered steel continuous casting blank as a raw material, and obtains a finished product 40MnV steel bar with the specification of 85mm through rolling production, and comprises the following steps:
step 1: cutting the continuous casting billet with the diameter of 300 multiplied by 400 multiplied by 9000mm, and putting the continuous casting billet into a heating furnace for reheating by adopting a cold conveying or red conveying mode.
Step 2: heating a steel billet: heating the steel billet by adopting a four-section heating mode, wherein the temperature of a preheating section is 590 ℃; heating to a first temperature of 1020 ℃; the temperature of the second heating section is 1130 ℃, and the process requirement is met; the temperature of the soaking section is 1150 ℃, and the process requirements are met; the total heating time in the heating procedure is 4.0h, and the soaking time in the soaking section is 78 min.
And step 3: descaling a steel billet: and descaling the heated billet by adopting high-pressure water to remove the scale, wherein the pressure of the high-pressure water is 50 MPa.
And 4, step 4: rough rolling of a steel billet: sending the descaled steel billets into a high-rigidity roughing mill for 6 frames for roughing to obtain rough rolling billets; the surface temperature of the rough rolling blank at the rough rolling inlet is 1050 ℃, the inlet temperature meets the process requirements, and the rough rolling pass is 6.
And 5: continuous rolling by a continuous rolling unit: sending the rough rolling blank obtained in the step 4 into a continuous rolling unit, and carrying out medium rolling and pre-finish rolling to obtain a rolled material with the specification of 100 mm; the surface temperature of the rough rolling blank at the middle rolling inlet is more than 900 ℃, the middle rolling pass is 6 passes, the pre-finish rolling outlet temperature is more than 850 ℃, and the pre-finish rolling pass is 4 passes.
Step 6: cooling through water: and (3) carrying out water cooling on the rolled material subjected to pre-finish rolling, and controlling the surface temperature of the rolled material to be 790 ℃. After water cooling, the rolled stock was red back to obtain the temperature for KOCKS rolling. In this example, the water cooling rate of the water-through cooling was 55 ℃/s, and the water pressure was 0.7 MPa.
And 7: and (3) KOCKS rolling: performing KOCKS rolling on the rolled material which returns to red after water cooling to obtain a bar material with the specification of 85 mm; the initial rolling temperature of the KOCKS rolling is 860 ℃, the temperature requirement of the KOCKS rolling mill is met, and the final rolling temperature is 545 ℃.
And 8: cooling by a cooling bed: and (4) rolling the bar material with the specification of 85mm obtained in the step (7), cooling the bar material with water for the second time, then feeding the bar material to a cooling bed at a low temperature, and performing air cooling on the bar material in the cooling bed to finally obtain a finished bar material. Wherein the temperature of the upper cooling bed is 500 ℃, the temperature of the lower cooling bed is 180 ℃, and the cooling speed is 25 ℃/min.
By adopting the rolling production method provided by the embodiment, the hot-rolled structure of the obtained 40MnV non-quenched and tempered steel bar is ferrite plus pearlite, the grain size is 8 grades, and the hardness is 295 HBW; the mechanical properties of the bar product are shown in table 1.
Example 3
The embodiment provides a rolling production method for improving the toughness of steel products on line, which takes a 40MnV non-adjusting steel continuous casting blank as a raw material to obtain a finished product 40MnV steel bar with the specification of 75mm through rolling production, and comprises the following steps:
step 1: cutting the continuous casting billet with the diameter of 300 multiplied by 400 multiplied by 9000mm, and putting the continuous casting billet into a heating furnace for reheating by adopting a cold conveying or red conveying mode.
Step 2: heating a steel billet: heating the steel billet by adopting a four-section heating mode, wherein the temperature of a preheating section is 580 ℃; heating to a first temperature of 1020 ℃; the temperature of the heating second section is 1120 ℃, and the process requirement is met; the temperature of the soaking section is 1150 ℃ and meets the process requirements; the total heating time in the heating procedure is 5h, and the soaking time in the soaking section is 65 min.
And step 3: descaling a steel billet: and descaling the heated billet by adopting high-pressure water to remove the scale, wherein the pressure of the high-pressure water is 50 MPa.
And 4, step 4: rough rolling of a steel billet: sending the descaled steel billets into a high-rigidity roughing mill for 6 frames for roughing to obtain rough rolling billets; the surface temperature of the rough rolling blank at the rough rolling inlet is 1000 ℃, the inlet temperature meets the process requirements, and the rough rolling pass is 6.
And 5: continuous rolling by a continuous rolling unit: sending the rough rolling blank obtained in the step 4 into a continuous rolling unit, and carrying out medium rolling and pre-finish rolling to obtain a rolled material with the specification of 90 mm; the temperature of the rough rolling blank at the middle rolling inlet is 920 ℃, the middle rolling pass is 6 passes, the temperature at the pre-finish rolling outlet is 890 ℃, and the pre-finish rolling pass is 4 passes.
Step 6: cooling through water: and (3) carrying out water cooling on the rolled material after pre-finish rolling, and controlling the surface temperature of the rolled material to be 780 ℃. After water cooling, the rolled stock was red back to obtain the temperature for KOCKS rolling. In this example, the water cooling rate of the water-through cooling was 55 ℃/s, and the water pressure was 0.7 MPa.
And 7: and (3) KOCKS rolling: performing KOCKS rolling on the rolled material which returns to red after water cooling to obtain a bar material with the specification of 75 mm; the initial rolling temperature of the KOCKS rolling is 840 ℃, the temperature requirement of the KOCKS rolling mill is met, and the final rolling temperature is 560 ℃.
And 8: cooling by a cooling bed: and (4) cooling the bar with the specification of 75mm obtained in the step (7) through second water penetration cooling, then feeding the bar to a cooling bed at a low temperature, and performing air cooling in the cooling bed to finally obtain a finished bar. Wherein the temperature of the upper cooling bed is 510 ℃, the temperature of the lower cooling bed is 180 ℃, and the cooling speed is 30 ℃/min.
By adopting the rolling production method provided by the embodiment, the hot-rolled structure of the obtained 40MnV non-quenched and tempered steel bar is ferrite plus pearlite, the grain size is 8 grades, and the hardness is 290 HBW; the mechanical properties of the bar product are shown in table 1.
Comparative example 1
According to the comparative example, the KOCKS conventional rolling process is adopted to prepare the non-quenched and tempered steel, the raw material of the non-quenched and tempered steel is a 40MnV steel continuous casting billet, and a finished product 40MnV steel bar with the specification of 50mm is obtained through rolling production, wherein the specific process parameters are as follows: the KOCKS finish rolling temperature is 850-900 ℃, and the temperature of the upper cooling bed is 700-800 ℃.
The 40MnV steel bar obtained by adopting the KOCKS conventional rolling process has the grain size of 5-6 grades and the hardness of 250-300 HBW, and the mechanical properties of the bar product are shown in Table 1.
In conclusion, the invention provides a rolling production method for improving the toughness of steel, which is unique, and the production method can be used for producing non-quenched and tempered steel with excellent comprehensive mechanical properties, and simultaneously greatly reduces the energy consumption of a heating furnace, thereby saving the production cost and protecting the natural environment.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Variations and modifications to these embodiments may occur to those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (10)
1. The rolling production method for improving the toughness of the steel on line is characterized by taking a continuous casting billet as a raw material and sequentially comprising the following working procedures: heating a blank, descaling, rough rolling, continuous rolling, water cooling, finish rolling of a bar reducing and sizing unit and cooling of a cooling bed to finally obtain a finished bar; wherein the content of the first and second substances,
in the bar reducing and sizing mill set finish rolling procedure, a rolled bar obtained in the water cooling procedure is subjected to finish rolling by using a bar reducing and sizing mill set to obtain a bar; the finishing temperature is 500-700 ℃.
2. The rolling production method according to claim 1,
in the blank heating procedure, the continuous casting blank is heated, the heat preservation temperature of the soaking section is 1100-1180 ℃,
preferably, in the blank heating procedure, the total heating time from the time when the blank enters the heating furnace to the time when the blank leaves the heating furnace is 4-6 h, the soaking time of the soaking section is 60-100 min,
preferably, the billet heating process is performed in a four-stage step-type heating furnace;
preferably, the raw material of the continuous casting billet is any one of 40MnV medium carbon steel, 42CrMo medium carbon steel, 45 medium carbon steel and 40Cr medium carbon steel.
3. The rolling production method according to any one of claims 1 to 2,
in the descaling procedure, high-pressure water is adopted for descaling to remove iron scales, and the pressure of the high-pressure water is 26-30 MPa; preferably 40 to 50 MPa.
4. A rolling production method according to any one of claims 1 to 3,
in the rough rolling procedure, the inlet temperature is 980-1050 ℃, and the rough rolling pass is 5-7; preferably, the roughing mill used in the roughing step has 6 stands in total, and the number of roughing passes is 6.
5. A rolling production method according to any one of claims 1 to 4,
the continuous rolling process comprises a middle rolling process and a pre-finish rolling process, and a rolled material suitable for entering the bar reducing and sizing mill set is obtained after continuous rolling; wherein the content of the first and second substances,
the inlet temperature of the middle rolling procedure is 900-950 ℃, and the middle rolling pass is 5-7; preferably, 6 middle rolling mills are arranged in the middle rolling process, and the middle rolling pass is 6 passes;
in the pre-precision rolling procedure, the number of pre-precision passes is 3-5; preferably, 4 pre-finishing mills are arranged in the pre-finishing rolling process, and the pre-finishing pass is 4 passes.
6. A rolling production method according to any one of claims 1 to 5,
in the water cooling procedure, the rolled material after continuous rolling is cooled to 650-850 ℃ by water, and preferably 650-800 ℃;
preferably, the water cooling speed of the through water cooling is 35-100 ℃/s, and the water pressure is 0.4-0.8 MPa;
preferably, after the through-water cooling, the rolled stock is red-backed to obtain the finish rolling temperature of the bar reducing and sizing mill set, so as to obtain the rolled stock suitable for finish rolling in the bar reducing and sizing mill set.
7. A rolling production method according to any one of claims 1 to 6,
in the finish rolling process of the bar reducing and sizing unit, the initial rolling temperature is 800-900 ℃;
preferably, the bar reducing and sizing mill group finish rolling is KOCKS rolling.
8. A rolling production method according to any one of claims 1 to 7,
the cooling bed also comprises second water through cooling before the cooling process; and the second water-through cooling is on-line water-through cooling.
9. A rolling production method according to any one of claims 1 to 8,
in the cooling process of the cooling bed, the temperature of the cooling bed on the bar is 480-650 ℃;
preferably, the cooling bed adopts a slow cooling mode, and the cooling speed of the cooling bed is more than or equal to 20 ℃/min;
preferably, in the cooling of the cooling bed, the surface temperature of the cooling bed below the bar is less than or equal to 200 ℃.
10. A rolling production method according to any one of claims 1 to 9,
the specification of the finished bar is 50-130 mm.
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